GB2207389A

GB2207389A - Manufacture of the themoplastics core of an optical communication cable

Info

Publication number: GB2207389A
Application number: GB08816274A
Authority: GB
Inventors: Clifford Heywood
Original assignee: Telephone Cables Ltd
Current assignee: Telephone Cables Ltd
Priority date: 1987-07-24
Filing date: 1988-07-08
Publication date: 1989-02-01
Anticipated expiration: 2008-07-08
Also published as: GB2207389B; GB8717578D0; GB8816274D0

Abstract

The thermoplastics core (1) is initially extruded with a circular cross-section and, following the cooling of the core, a plurality of sinusoidal grooves (11) for accommodating optical fibres are formed in the periphery of the core by means of heated conductors, for example in the form of forming wires (5), which are disposed into the sinusoidal configuration by continuous passage through openings (8) of an oscillating lay plate, and pressed into the core surface on passage with the core (1) through a cooled die (9), and then removed from the solidified themoplastics to leave the grooves impressed in the core. The conductors are preferably induction heated. The heated groove forming conductors may alternatively comprise the nip of co-operating endless belts (15, Fig.3), or rollers, having sinusoidal ridges which form the grooves. <IMAGE>

Description

Manufacture of Communication Cables This invention relates to the manufacture of a communication cable of the kind containing a multiplicity of optical fibres. It is important that the design of such an optical communications cable allows for stretching to occur (which may arise during manufacture or usage) without damage to the optical fibres or an increase in signal attenuation. Therefore, the optical fibres must have excess length and be suitably housed in a manner to avoid micro-bending. This can be achieved by locating one or more of said optical fibres in each of a number of similar grooves arranged around the periphery of a core of thermoplastics material, and extending along the core in a periodically reversing helical fashion, hereinafter referred to as "sinusoidal", although it will be appreciated that the grooves need not be strictly of mathematically sinusoidal shape.

The invention relates, in particular, to the manufacture of a thermoplastics core for an optical communications cable having a multiplicity of longitudinal sinusoidal grooves spaced around the circumference of the core.

According to the invention, in the manufacture of a thermoplastics core for a communications cable, the core is initially extruded with a circular cross-section and, following the cooling of the core, a plurality of grooves are impressed into the surface of the core around its periphery, so as to extend sinusoidally along the core, by means of heated conductors pressed against the core surface.

This can be achieved in a variety of ways. Thus the extruded core may be passed through a central opening in a member arranged to oscillate about the core axis, while heated wires are passed through respective openings spaced around the member and subsequently pressed into the surface of the core, the core being then cooled to solidify the plastics material around the wires, and the wires then removed to leave the sinusoidally extending grooves in the core surface.

The wires, which may be heated by induction heating coils, may be fed through the oscillating member, which conveniently comprises a lay plate, from bobbins.

Alternatively, however, continuous loops of wire may be used the wires being straightened before being reheated and fed again through the oscillating member.

In another way of forming the grooves two or more endless bands formed with sinusoidal ridges, having an appropriate number and cross-section formed in their surfaces, may be preheated and progressively formed into a circular shape around, and travelling with, the core, the bands being pressed against the surface of the core so as to form said grooves therein. The bands may have sinusoidal edges which follow the configuration of the grooves.

In yet another manner of forming the grooves the cooled circular core is passed between heated rollers, having forming surfaces with sinusoidal ridges formed therein, the forming surfaces of the rollers encircling the core so as to impress correspondingly shaped grooves in the core surface, the core surface being cooled immediately it emerges from between the rollers, as by means of cooling fluid, either in gaseous or liquid form, directed on to the core for example by means of suitably positioned nozzles.

Following the formation of the grooves by any of the methods above described, optical fibres are introducd into the grooves in any suitable manner, and one or more protective coverings then applied around the core in accordance with known manufacturing techniques.

Three different methods of forming grooved cores in the manufacture of optical fibre cables will now be described by way of example with reference to Figures 1 to 4 of the accompanying schematic drawings, in which Figure 1 illustrates in diagrammatic form apparatus for carrying out one of said methods, Figure 2 illustrates, also diagrammatically, a modification of the apparatus shown in Figure 1 for carrying out the second method, and Figures 3 and 4 illustrate a further apparatus and a section thereof respectively for carrying out the third method.

In the method illustrated in Figure 1, a core 1 of thermoplastic material, such as polyethylene, with or without a centrally located metallic or non metallic strength member, is extruded with a smooth circular cross-section, using conventional plastic extrusion equipment 2.

The extruded core is allowed to cool and is then passed through a central opening 3 in an oscillating lay plate 4.

A plurality of metal wires 5 (only two of which are shown), having a circular, square or rectangular cross-section of appropriate dimensions for forming the required grooves in the core surface, are contained on bobbins 6 disposed around the core. Each wire, which could be either a ferrous or a non-ferrous metal, is fed through an induction heating coil 7 and through a respective one of a number of equally spaced holes 8 in the oscillating lay plate 4.

The inductionally heated wires 5, after leaving the lay plate 4, and thus aligned around the circumference of the circular-sectioned plastics core, pass with the core into a die 9 which causes the wires to be pressed into the core surface. The die 9 may be suitably cooled to cause the plastics material to solidify rapidly around the wires, which are subsequently removed from the core leaving sinusoidal grooves impressed into the core surface as at 11. Consideration of the die design should be made to allow for the plastics material displaced by the insertion of the wires. The wires can then be wound onto further bobbins as at 12, and may subsequently be re-used, after cleaning if necessary.

Following the formation of the grooves 11 one or more optical fibres, either separately or formed into bundles or strips, are fed into them, and the cable completed by surrounding the coil with one or more protective covers in accordance with known manufacturing techniques.

The extrusion of the core, the impression of the grooves, the introduction of the optical fibres and the application of the protective cover or covers can all be carried out as a continuous in-line process, although this need not necessarily be the case.

Thus the core may be extruded and stored, prior to the formation of the grooves therein. Similarly the grooved core can be stored before the optical fibres are introduced and the cable completed.

An alternative process, illustrated in Figure 2, is similar to that already described, with the same parts denoted by the same reference numberals, except that in this case the groove-forming wires consist of continuous loops as at 13 carried by rollers 14, the wires being straightened after completing the forming operation, for example by further rollers 14A, and before re-entering the heaters 7 and oscillating lay plate 4.

Where the pitch of the sinusoidal grooves 11 formed by either of the two methods described above is relatively short it will be necessary for the wires 5 or 13, as the case may be, to be pressed into the plastics core 1 within-a very short distance of the oscillating lay plate 4 as illustrated, to avoid loss of amplitude during reversal.

In a third process illustrated in Figures 3 and 4 the grooves 11 are formed in the extruded core 1 by means of two or more continuous flexible metal belts 15 having sinusoidal ridges 16, of an appropriate cross-section and number, extending inwards from the inner surface of each belt.

As in the case of the wires of the previously described processes, the belts 15 are heated to the required temperature, for example by passage through respective induction heaters (not shown) and are progressively formed into circular shape around and travelling with the core 1 by means of appropriately shaped and positioned rollers 17. During the groove-forming operation the heated belts 15 are pressed into the surface of the plastics core 1, by means of rollers 18 and any excess material squeezed out between the belts and subsequently removed. The belts themselves have sinusoidal edges to follow the configuration of the grooves, and are contained in the circular form with cooling as required until the groove sections are permanently formed. As before optical fibres are subsequently fed into the formed grooves in any convenient manner, and the cable completed by the application of one or more protective covers.

In a modification of this latter arrangement, not illustrated, the grooves are formed in the plastics core by passing the core through co-operating heated rollers having concave shaping surfaces arranged to completely encircle the core and formed with sinusoidal appropriately shaped and positioned ridges which are pressed into the core surface. In this case means must be provided for rapidly cooling the core immediately it leaves the rollers to maintain the shape of the formed grooves as by directing cooling fluid, either in liquid or gaseous form on to core surface through suitably shaped and positioned nozzles.

Claims

1. The manufacture of a thermoplastics core for a communications cable of the kind referred to, wherein the core is initially extruded with a circular cross-section and, following the cooling of the core, a plurality of grooves are impressed into the surface of the core around its periphery, so as to extend sinusoidally along the core, by means of heated conductors pressed against the core surface.

2. The manufacture according to Claim 1 wherein the extruded core is passed through a central opening in a member arranged to oscillate about the core axis, while heated wires are passed through respective openings spaced around the member and subsequently pressed into the surface of the core, the core being then cooled to solidify the plastics material around the wires, and the wires then removed to leave the sinusoidally extending grooves in the core surface.

3. The manufacture according to Claim 2 wherein the wires are heated by induction heating coils.

4. The manufacture according to Claim 2 or 3 wherein the oscillating member comprises a lay plate.

5. The manufacture according to Claim 2, 3 or 4 wherein the wires are fed through the oscillating member from bobbins.

6. The manufacture according to Claim 2, 3 or 4 wherein the wires are in the form of continuous loops and are straightened after their removal from the core surface, and prior to being reheated and fed again through the oscillating member.

7. The manufacture according to Claim 1 wherein two or more endless bands formed with sinusoidal ridges, having an appropriate number and cross-section formed in their surfaces, are preheated and progressively formed into a circular shape around, and travelling with, the core, the bands being pressed against the surface of the core so as to form said grooves therein.

8. The manufacture according to Claim 7 wherein the bands are formed with sinusoidal edges which follow the configuration of the grooves.

9. The manufacture according to Claim 1 wherein the cooled circular core is passed between heated rollers, having forming surfaces with sinusoidal ridges formed therein, the forming surfaces of the rollers encircling the core so as to impress correspondingly shaped grooves in the core surface, the core surface being cooled immediately it emerges from between the rollers.

10. The manufacture according to Claim 9 wherein the cooling of the core after its emergence from between the rollers is achieved by a cooling fluid, either in gaseous or liquid form, directed on the core surface.

11. The manufacture of a thermoplastics core for a communications cable of the kind referred to carried out substantially as shown in and as hereinbefore described with reference to Figure 1 or 2 or Figures 3 and 4 of the accompanying drawings.

12. Apparatus for manufacturing a thermoplastics core for a communications cable of the kind referred to by the method of Claim 1 comprising an extruder for initially extruding the core with a circular cross-section, a plurality of conductors, means for heating the conductors to a temperature above the softening temperature of the material of the core, means for pressing the heated conductors against the core surface, the conductors being shaped to impress sinusoidal grooves into the core surface, and means for subsequently removing the conductors from the grooved core.

13. Apparatus for manufacturing a thermoplastics core for a communications cable of the kind referred to substantially as shown in and as hereinbefore described with reference to Figure 1 or 2 or Figures 3 and 4 of the accompanying drawings.

14. A communications cable of the kind referred to having a core of thermoplastics material manufactured according to any one of Claims 1 to 11.